In order to measure water usage by various users in a system, each user is provided with a water meter in their water supply line, which measures and records the quantity of water passing through the meter. This measured quantity can be used by the user to track his usage, as well as by the local water supplier, such as a town, for billing purposes.
In many buildings there are leaks and other water demands at low volumes which are too small to be measured by the meter. However, since these flows continue all day long, the unmeasured usage can reach up to 15% of the total water supplied to that building. Traditionally, this problem is dealt with by using a higher class of metering system, i.e., from Class B to Class C, or even class D. Each measurement class has advantages and disadvantages. Moving from class A to higher classes dramatically improves the ability of the meter to measure low flux. However, the reliability of function of the meter becomes more problematic with each higher class, as does the cost of utilizing the system.
Another way to deal with this problem is to utilize meters of smaller diameter, i.e., reduce from ¾″ to ½″. In this way, the ability to measure low flux is increased, since the smaller the diameter, the lower the value of the nominal volume at which the meter will work for a long time without breaking down. The disadvantage of this method is that the pressure drop across the water meter at a given flow increases in inverse proportion to the diameter. Thus, smaller diameter pipes are likely to create an unacceptable pressure drop across the meter. Furthermore, reducing the diameter of the pipe, and the resultant reduction in pressure, is likely to result in a loss of water pressure to the consumer. To prevent this loss of pressure, larger pipes are required at a higher supply pressure. This means much higher costs of infrastructure and wasted energy resulting from the loss of pressure across the meter. Thus, while these methods may reduce somewhat the problem of unmeasured water flow, they do not provide a satisfactory solution, and cause additional problems.
A number of different kinds of water meters are in use today, multi-jet, single-jet, positive displacement, hydraulic oscillation meter, and so on. The range of flow or volume measurement of each meter is defined according to the following parameters and illustrated in FIG. 1. FIG. 1 is a graph illustrating the percentage measurement error over flux Q of a conventional water meter. Qstart is the flux at which the meter begins to respond to the volume flowing through it. Measurement errors are likely to be tens of percent. As can be seen, there is a range between 0 and Qstart where the meter stops, as it is unable to measure at all. From a minimum flux Qmin to a higher flux Qt (Qtransition), about ±5% error is acceptable. At Qt (Qtransition) the acceptable percent error of the measurement cannot be higher than ±2% error. As can be seen, from Qt to Qmax (the maximum flux possible through the meter with a pressure drop of less than 1 atm), the measurement is in the optimum range of less than ±2% error. As can be seen, in such a meter, a slow leak Qleak resulting in a slow, small volume flow, is likely to be lower than Qstart or Qmin, and would not be detectable at all by the meter.
Conventional meters were designed to measure over a wide range of flux. However, this means that at the high and low ends of the range, the measurement is extremely inaccurate, if measured at all. In order to provide more accurate measurement over a particular range of flux, the combination meter was developed. A combination water meter includes a main meter which can be connected to a water main for determining larger amounts of water flow and to an auxiliary meter which is disposed in a bypass conduit for determining smaller amounts of water flow. These devices generally are very expensive to manufacture and maintain.
A mechanical device for preventing unmeasured quantities of fluids from passing the meters is illustrated in GB Patent 2083 to Meineke. This patent describes a meter having a main and a service pipe with a variable resistance placed between them. The device includes a valve between the main and the service pipe, which is acted upon by a slotted lever weighted by a rolling weight. When the weight is in the outward position, the resistance to the passage of fluid is great, but as the fluid pressure decreases in the service pipe, the valve and the lever are raised so that the weight slides to the other end of the slot, and the resistance diminishes, thus allowing a sudden opening of the valve.
There are known valves using a permanent magnet and a movable poppet attracted by a magnetic field. Generally, the poppet is round and held by the magnet in the valve seat until sufficient pressure is created to move it from the valve seat and open the valve. One such valve mechanism is shown and described in EP patent publication 925465. This application describes a pressure-opened and magnetically closed valve mechanism for fluids having a sealing body having at least one circular cross-sectional area sized to be wedged in the opening of the valve mechanism.
Another example of such a device is shown in U.S. Pat. No. 5,320,136 to Morris et al. This patent describes a magnetically operated check valve having a valve body, a movable poppet disposed therein and a magnet. When the liquid pressure acting on the poppet is below a minimum threshold, the poppet is attracted to the magnet, closing off the pipe. If a slow flow of liquid continues, the liquid is collected and held by the poppet until the pressure of the collected liquid exceeds the magnetic force, unseating the poppet to an open position. This poppet and magnet are configured to trap magnetically attracted particulates and prevent them from flowing to the valve seating region.
In these conventional valves, movement of the poppet immediately opens the valve seat over a relatively small surface area, permitting a small flow of liquid through the valve until equilibrium is reached between magnetic force attracting the poppet and decreasing fluid pressure acting on the poppet, until the poppet no longer moves away from the valve seat. Thus, these valves do not provide sufficiently large flows for measurement by conventional water meters.
Conventional magnetic valve mechanisms are designed to achieve equilibrium in the open position. Thus, when the fluid pressure overcomes the force of the magnetic field, the poppet is moved from the valve seat, creating a small fluid flow opening and a slow reduction in pressure. At the same time, as the poppet moves, the force of the magnetic field is reduced, and equilibrium is reached with the poppet in the open position, as long as there is a relatively fixed fluid flow through the valve above the threshold value.
There is also known, from U.S. Pat. No. 6,317,051, a water flow monitoring system for determining the presence of leaks in plumbing pipes having water flowing through the pipes under high pressure. The system includes a flow monitor which is mounted to the pipe, a controller composed of a timer or an accumulated volume meter to determine when the flow has continued for a pre-selected period of time or when the amount of water has exceeded a pre-selected accumulated volume threshold, and logic components respond to changes in the flow rate, at which time, a valve is actuated to stop flow through the pipe. This solution is very complicated and expensive to manufacture and maintain.
Accordingly, there is a long felt need for a device which concentrates low volumes of fluid and prevents fluid flow until there is a sufficient volume to be released as measurable flux, which can be measured in a conventional meter with an acceptable percentage error, and it would be desirable that such a device would close the flow passage rapidly when the fluid pressure acting on it drops.